The present invention relates, in general, to the field of laser-based rangefinding and distance measuring instruments such as laser rangefinders and tape laser devices. More particularly, the present invention relates to a self-aligned aiming system and technique for a laser rangefinder incorporating a retroreflector.
In order to measure the distance to a target with a laser rangefinder or tape laser device, the user generally first aims a visible laser beam toward the target or object to place a visible dot on a specific point. The user then triggers the instrument to measure the distance to that point by analysis of the reflected laser energy from the target returned to the rangefinder. The distance to the target is then calculated and displayed by the rangefinder. In the case of tape lasers, the instrument is placed where the user would otherwise hold a tape measure and the dot is aimed at the point to which the tape would be extended.
In those instruments having an observation port, it is important that the virtual dot observed by the user in the rangefinder viewing window be in alignment with the visible laser beam, particularly in precision applications. Any parallax between the virtual dot and the visible laser beam can potentially introduce errors into the measurement. Conventional optical systems attempting to minimize this parallax rely on difficult and time consuming alignment of the instrument's optical components. In practice, such alignment procedures are expensive, subject to error, variation due to temperature and other environmental factors and the instrument can ultimately be rendered misaligned due to sustained usage or impacts.